1. Field of the Invention
Example embodiments of the present invention relate in general to an apparatus and a method for removing a photoresist structure from a substrate.
2. Description of the Related Art
In general, semiconductor devices are manufactured by performing several processes. One process is a fabrication process for forming an electrical circuit on a silicon wafer that is used as a semiconductor substrate. An electrical die sorting (EDS) process is performed for inspecting electrical characteristics of the semiconductor devices formed by the fabrication process. A packaging process is then performed for packaging the semiconductor devices in epoxy resins and individuating the semiconductor devices.
In the fabrication process, a photoresist structure is formed on the substrate by a photolithography process. The photoresist structure is patterned by the photolithography process to form a photoresist structure on the substrate as a mask pattern for a subsequent process. For example, an etching process is performed on the substrate using the photoresist structure as an etching mask, so that an electric circuit is formed on the substrate. The photoresist structure is then removed from the substrate.
An ozone ashing process using ozone (O3) gas and a light ashing process using a light are typically performed to remove the photoresist structure from the substrate. In the ozone ashing process, a heated gas including ozone (O3) is supplied onto the photoresist structure, and a thermal decomposition process is generated in the photoresist structure by the gas including ozone (O3). This removes the photoresist structure from the substrate. In the light ashing process, ultraviolet rays simultaneously break chemical bonds in the photoresist structure and change ozone (O3) gas into activated oxygen (O2) gas. The activated oxygen reacts with the photoresist structure having its chemical bonds broken by the ultraviolet rays, so that oxidation decomposition occurs in the photoresist structure to make the photoresist structure strongly volatile. Due to this strong volatility, the photoresist structure is removed from the substrate.
Generally, the chemical reaction between the ozone gas and the photoresist structure on the substrate tends to occur more actively at high temperatures. Thus, the higher the temperature in the substrate, the more active the chemical reaction of ozone and the photoresist structure. However, the higher the temperature of the substrate, there is also a problem in that there is an increased chance of generating defects in the formed semiconductor devices.
For the above reason, the photoresist pattern is removed from the substrate at a relatively low temperature. However, the low temperature in the substrate may markedly reduce the removal rate of the photoresist structure.
In the above conventional ozone ashing process and in an effort to alleviate problems due to the low temperature, water vapor is added to the ozone (O3) gas so as to improve the removal rate of the photoresist structure in spite of a low temperature of the substrate.
A mixture of ozone (O3) gas and water vapor is supplied to a first side of a substrate mounted on a susceptor and is exhausted from a second side of the substrate opposite to the first side. Because the mixture of ozone (O3) gas and water vapor is added to the photoresist structure at a high thermal state, the mixture has a higher temperature when added to the photoresist structure, than when it is exhausted from it.
Accordingly, much more of the photoresist structure adjacent to the first side of the substrate is removed than that adjacent to the second side of the substrate. This is because the photoresist structure adjacent the first side of the substrate is at a higher temperature than the photoresist structure adjacent to the second side of the substrate. As a result, the photoresist structure is not removed uniformly from the substrate.
To overcome the above-mentioned problem, the mixture of water vapor and ozone (O3) gas is added to a processing chamber and uniformly distributed onto the substrate including the photoresist structure. This is done through a showerhead installed at a top portion of the processing chamber. The mixture of water vapor and ozone (O3) gas is uniformly distributed onto the substrate including the photoresist pattern through the showerhead, and the temperature in the photoresist pattern is substantially maintained at a constant. Hence, the photoresist pattern is more uniformly removed from the substrate.
However, using a mixture of water vapor and ozone (O3) gas to bring about a uniform removal of the photoresist structure may cause other problems. Since the substrate including the photoresist structure is heated to a high temperature, the water vapor in the mixture is condensed and then is instantaneously vaporized. Consequently, the mixture makes contact with the heated substrate, which is known in the art as a spot phenomenon. Accordingly, a watermark, which is a trace of a water drop due to the spot phenomenon, remains on the substrate to cause defects in subsequent processes.